Hundreds of automatic garage doors in the Ottawa area have suddenly and strangely stopped working, due to a powerful radio signal that appears to be interfering with their remote controls.

The phenomenon began suddenly last weekend, J.P. Cleroux of Ram Overhead Door Systems said, adding that a strong signal was blocking garage door openers.

Angolan Ambassador Miguel Puna couldn't close the embassy's iron gates using his remote control Thursday.

"It's affects a 25-mile radius. That's huge," said Cleroux.

Angolan Ambassador Miguel Puna is one of those affected by the problem. He can no longer open his embassy's electronic gate.

"Not only in this gate, but even other gates, we are having a lot of problems," said Puna. "This could cause security concerns."

Cases have been reported from as far away as Casselman and Aylmer, but two companies that have plotted the reported problems on maps say they appear to cluster in the Byward Market area and a corridor leading south-east from there.

The Door Doctor has received more than 100 calls from irate customers who can't operate their doors using the remote. It installs Liftmasters, one of the most popular door openers in North America, which operates by radio frequency.

The signal is transmitted on the 390-megahertz band, which is used by virtually all garage door openers on the continent.

It's the same frequency used by the U.S. military's new state-of-the-art Land Mobile Radio System.

Cleroux says operators have already been warned of this phenomenon by service updates from U.S. manufacturers, who started seeing the same problem around military bases last summer. The strong radio signals on the 390-megahertz band simply overpower the garage door openers.

One technician likened it to a whisper competing with a yell.

"From what we hear, it is the American Embassy that's operating on 390, and they're the only ones who can block it, but I'm not 100 per cent sure, because we're all kind of up in the air until we know exactly what's going on," said Cleroux.

The U.S. Embassy denies any transmissions on that frequency. So does the Canadian military.